Conventionally, diesel engines include exhaust gas recirculation (EGR) devices that introduce some exhaust gas to intake passages to reduce NOx contained in the exhaust gas (e.g., refer to Patent Document 1). An EGR device includes an EGR valve in an EGR passage that connects an exhaust passage to an intake passage and adjusts the amount of EGR gas introduced to the intake passage by controlling the opening degree of the EGR valve.
In recent years, various types of techniques have been proposed that determine the presence or absence of anomalies in an EGR valves using an on-board diagnostic system (OBD), which is installed in a vehicle. As an example of anomaly determination techniques, a technique is known that determines the presence or absence of an anomaly in an EGR valve with respect to responsiveness, which is a change in the EGR valve relative to a change in an opening degree instruction value to the EGR valve. The presence or absence of an anomaly of responsiveness can be determined by measuring the EGR amount when the EGR valve is opened and closed in a no-load state, in which the pressure of the intake passage and the pressure of the exhaust passage are stable.